Oil or gas drilling tool block with textured coating

ABSTRACT

An oil or gas tool block with an advanced textured coating produced by automated electro spark deposition equipment. A die insert includes a substrate onto which a gripping surface is formed. The gripping surface is a textured coating electro-deposited on the substrate. The textured coating includes a cobalt-based alloy supplied directly by the welding electrode, allowing the continuous build-up of material typically in the range of 0.001-0.040 inches. The cobalt-based alloy comprises a blend of chromium, cobalt, iron, manganese, molybdenum, nickel, and silicon. One or more die inserts, whether blank or textured, can be stacked to form a tool block. In a process for making the die insert, the substrate is texture-coated using electro-spark deposition in two passes, including a first coating pass and a second coating pass. Hard coating may follow to thereby form a gradient of layers.

CROSS-REFERENCE TO RELATED APPLICATIONS

The instant application claims benefit of provisional application Ser. No. 61/897,989 filed Oct. 31, 2013, the contents of which are incorporated herein by reference.

BACKGROUND

Oil and gas drilling involves handling and gripping pipe. Spider and elevator systems are used to hold the casing, liner or completion string in place during running The spider and elevators are equipped with slips, which consist of dies. The dies penetrate into the surface of the pipe upon activation such that the spider or elevator systems hold the weight of the pipe string.

Other handling systems include power tongs, which are hydraulically-powered gripping tools suspended above the rig floor. As with slips, tongs produce permanent marks on pipe body and tool joints. The gripping system marks develop high stress concentration that reduces strength of the pipe, which can lead to tubular failure. Additionally, die marks support corrosion, further decreasing the life of the pipe.

The dies themselves are also subject to premature wear and short life spans. Traditional dies are made by brazing and machining methods. For instance, the die in U.S. Patent Publication 2004/0207223 to Bee et al. describes nickel plated, knurled teeth. U.S. Pat. No. 5,971,086 to Bee et al. additionally describes uniform teeth. Although the teeth or grooves do not have to be uniform, various textured, particle coatings used for these dies are still traditionally formed by using a metal matrix or brazing alloy. U.S. Pat. No. 7,036,397 to Bangert shows a granulated particle coating for dies formed by using a metal matrix or brazing alloy.

Machining “teeth” into a metal surface is slow and requires expensive machine tools and a highly skilled operator. Moreover, machined “teeth” tend to wear and fracture in service, so they are not durable. Brazing a hard phase onto a drill tool involves expensive filler material and requires an expensive multi-step production process, including a vacuum heat treatment. The brazed coating is relatively thick, and the particles are not metallurgically bound, so they can pull out of the coating in service. It has also been found that brazed texture coatings can delaminate from the block in service. Finally, the heat treatment (braze cycle) changes the mechanical properties of the tool block.

There is a need then for a superior die insert and tool block with a surface texture which increases the coefficient of friction between the pipe and the tools, while minimizing damage to the pipe. In general, the state of the art means to produce textured surfaces on oil and gas drilling tools are expensive to apply and the products have limited service life. In addition, when the tool blocks must support a large weight (a long drill string), the limited strength of state of the art tool block texture coatings requires the use of a large number of blocks. Therefore, there is an additional need for a tool block with a stronger texture coating than state of the art tool blocks, and consequently, fewer tool blocks would be required to support the same load.

SUMMARY

It is the objective of the instant invention to provide a die insert having a gripping surface which increases the coefficient of friction between the pipe and the tools, while minimizing damage to the pipe.

It is further an objective to provide a die insert which includes a textured coating which is cost-effective to apply.

It is further an objective to provide a product which does not have as limited a service life as traditional gripping systems.

It is further an objective to provide a tool block with a stronger texture coating than state of the art tool blocks, and consequently, fewer tool blocks would be required to support the same load.

Accordingly, the invention comprehends a die insert, including a substrate onto which a gripping surface is formed. The gripping surface is a textured coating which is electro-spark deposited on the substrate. The textured coating includes a cobalt-based alloy comprising a blend of nickel, molybdenum, iron, silicon, and cobalt. The coating is supplied by a welding electrode (rod) as part of the electro-spark deposition process.

A tool block comprising one or more of the die inserts, which comprises multiple substrates, wherein at least one of the substrates is a die blank and at least one of the substrates is a textured substrate having a gripping surface. As such, the substrates can be stacked to form a tool block, wherein the die blank and the textured substrate are stacked in alternation both vertically and horizontally. Again, the gripping surface of the textured substrate is formed by being electro-spark deposited on the substrate.

In a process for making the die insert, the substrate is texture-coated using electro-spark deposition in two passes, including a first coating pass and a second coating pass. The first coating pass further comprises the steps of aligning the substrate on a magnet of an ESD equipment including an electrode; inserting a welding rod into the equipment; setting an applicator angle in relation to the substrate; and, coating the substrate with the welding rod. In the second coating pass the applicator angle is changed. Lastly, the die insert is hard-coated.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a perspective view of a pipe slip containing the instant die inserts formed as a tool block.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference then to FIG. 1, shown is the tool block within a slip assembly 10 comprising one or more die inserts 14. Electro Spark Deposition (ESD) equipment is utilized and is critical. ESD equipment means automated or hand-operated, localized welding machines including welding rods and/or welding electrodes. ESD is a localized welding process. The ESD electrodes, as further described, consist of hard particles in an alloy matrix. An arc is struck for a short time (milli-seconds) in a small area. The arc melts the rod matrix and the substrate surface, plus the hard particles begin to dissolve in the weld pool (molten metal). When the arc is terminated, the molten pool solidifies rapidly creating an alloy steel surface layer containing the metallurgically bound hard particles. The ESD process is fast and it is automated, so a consistent high quality coating can be produced with a minimum of labor. Since the weld is small, there is only insignificant heating of the substrate, and consequently, the ESD process does not change the properties of the substrate. Finally, since the hard particles are dissolving when the pool freezes, they are an integral part of the alloy surface layer, yielding a strong bond.

Tool block as used herein means one or more die inserts 14. Die insert 14 as used herein means an insert for devices used to grip tubular members, including but not limited to slip and elevator assembly, power tongs, and conventional slip systems. Typically these systems reside above the rig floor. As an example only and not meant to be limiting, shown by FIG. 1 is a tool block for a slip assembly 10, although the die inserts 14 can be used in any type of the aforementioned systems and can vary in number. “A” as used in the claims means one or more.

With continued reference to FIG. 1, the tool block, or one or more die inserts 14, are typically retained in a die retaining cavity 11 of the slip assembly 10. The instant die insert 14 is formed using ESD and comprises a substrate 12 and a gripping surface 18 on the substrate 12. The substrate is preferably steel, such as a medium-carbon 1045 steel or carburized 8620. Die retaining cavity 11 means any type of slip bowl, elevator bowl, or surface thereof. As is known, the substrate 12 conforms to the shape of die retaining cavity 11 and thus the slip assembly 10, and, when secured therein, the gripping surface 18 of the die insert 14 is held in the direction facing the pipe surface.

Gripping surface 18 formed on substrate 12 is a textured coating, thereby forming a textured substrate. The textured coating is electro-deposited on the substrate 12 using the ESD equipment. The composition of the electrodes is critical to production of superior textured coatings on oil and gas drilling tools for two reasons. First, the strength, toughness and hardness of the second phase particles can be critical to tool service life. Although metal carbides are typically used, metal borides and nitrides have superior properties in many oil and gas tool applications. Second, the composition of the electrode matrix influences the composition of the weld pool, and consequently, the properties of the alloy surface layer (coating matrix). Accordingly, in the preferred embodiment the textured coating includes a cobalt-based alloy comprising a blend of chromium, cobalt, iron, manganese, molybdenum, nickel, and silicon. The composition of the electrodes (metal matrix or hard phase) can be changed to modify the mechanical and corrosion properties of the textured surface for various applications. However, in the preferred embodiment herein as it relates specifically to the requirements for use as tool block, the cobalt-based alloy blend consists of in the ranges of 15-40% chromium, 40-70% cobalt, 1-5% iron, 0.1-1.0% manganese, 3-7% molybdenum, 1-5% nickel, and less than 1.0% silicon. This analysis is a guideline only and may not account for incidental elements. This blend is supplied by the welding electrode. “Supplied” means the blend comes directly from the rod or electrode. The blend's formation as a rod critically allows the continuous build-up of material allowing for a textured coating deposit thickness typically in the range of 0.001-0.040 inches, preferably 0.030-0.035 inches. Use of the instant blend allows for this particular thickness. A carbide rod, for instance, could not build up to that thickness. This process is further described below.

When multiple substrates 12 and die inserts 14 are stacked, a tool block is formed. The tool block does not require that all surfaces thereon include gripping surfaces 12. With continued reference to FIG. 1, shown are multiple substrates 12, wherein at least one of the substrates 12 is a die blank 16 and at least one of the substrates 12 includes the gripping surface 18, i.e. the textured coating electro-spark deposited on the substrate 12. In the instant embodiment, each die blank 16 and each textured substrate (substrate 12 with gripping surface 18) are stacked in alternation within the die-retaining cavity 11. “Stacked” means separate blocks abut one another in any direction, or separate surfaces (blank or textured) are formed on a single block, thus the number of surfaces and blocks may vary according to the slip assembly design. “Alternation” as used herein means a die blank 16 (without a textured coating) is adjacent to a textured substrate in the horizontal and/or vertical direction in a repeating pattern, although it should understand a pattern is not required, rather critical is that at least one die blank 16 can be used adjacent to a textured substrate. This is made possible due to the superior qualities and coefficient of friction of the textured substrate. By not requiring all substrates 18 be texture-coated, manufacturing costs are reduced. The textured coating of the invention is stronger than state of the art products so fewer blocks are required to support a given load. Additionally, less surface texture on the pipe resulting from having fewer textured substrates further results in less damage to the pipe.

For the process of making the instant die insert 14 with gripping surface 18, a substrate 12 as above is texture-coated by electro-spark deposition using ESD equipment. The coats occur in two passes plus a hard coating step. Specifically, for the first coating pass, the substrate is aligned on the ESD equipment, for instance on a magnet therefor. The ESD equipment includes an electrode or welding rod, the composition of the welding rod described above as the cobalt-based alloy. The welding electrode is inserted into the ESD equipment. Critically, the welding electrode must be set at an angle. It has been found that setting the applicator angle of the electrode for the first coating pass in the range of 30-40 degrees, optimally 34.5 degrees, in relation to the substrate results in a superior deposit. Thus, at this angle the substrate is coated with the welding electrode.

The second coating pass comprises the step of maintaining the substrate on the magnet, but here the applicator angle is set in the range of 15-25 degrees, optimally 19 degrees in relation to the substrate. The substrate is then again coated with the welding rod. Angle changes between passes are done as a way to improve coverage as the first pass leaves porosity. The angle is changed to ensure bonding and produce as dense and consistent a deposit as possible.

Lastly, the substrate is hard-coated with a refractory metal carbide, namely a C2 tungsten carbide electrode. The hard-coating pass can be set as a third, automated pass of the ESD equipment or can be manually applied for smaller lots. The hard-coating dissolves even harder carbides into the textured coating making it more durable. Importantly as well, the final product from substrate to hard coating is formed as a gradient, varying in hardness from substrate to texture coating to hard coating. This gradient change critically allows the strong bonding of the various layers because a very hard layer is difficult to bond to very soft layer. In the preferred embodiment, depending on grade specifications, the hard coat electrode and therefore the hard coat composition consists of in the ranges of (by weight) 40.0-97.7% tungsten carbide, 3.0-30% cobalt, 2.0% or less tantalum carbide, 5.1% or less chromium carbide, 4.5% or less chromium, and 5% or less vanadium carbide.

EXAMPLE

An extensive load test program on die blocks holding steel or chromium drill pipe was conducted to compare and contrast state-of-the-art brazed product and the instant ESD product, i.e. two, rough-coated die inserts.

A load test was conducted in Houston, Texas using 4.5 inch diameter drill pipe made of either steel (T110) or chrome (CRA) material. Two texture coatings were evaluated. These include: GF is a commercially available die insert using a texture coating produced using a high temperature braze process, and GG is the instant coating manufactured using electro spark deposition. The tests were conducted on a SES vertical load frame configured for sixty inches of stroke and up to one million pounds of load. The rig configuration involved a solid API #3 bowl and a bite mandrel to insure sufficient cross-sectional area to allow the coated slips to be loaded to the full capacity of the drill pipe. For each coating and pipe combination a sample was loaded to eighty or one hundred percent of the pipe load capacity, giving a total of eight tests. Following the load tests, the depth of penetration of the die marks into the tube wall was measured for each of the eight samples. These measurements were used to insure that none of the marks exceeded the maximum damage allowed by American Petroleum Institute (API) standards (5% of wall thickness), and to compare the damage caused by the two different coatings. The results of the tests are summarized, as follows.

The results of the coating load tests include measurements of die mark penetration into the tube wall for each trial and photographs of the tube surface for each of the eight trials (not shown). The die mark penetration measurements are summarized in Table 1, and examination of this table reveals that none of the die marks exceed the maximum allowed by the API. In addition, the GG coating performed better than the GF coating at both loads and for both tube materials considered.

TABLE 1 Depth of Depth of Tube Die Penetration Penetration Style Used Load (Min/Max) (Average) T110 GG 80% .002″ .002″ T110 GG 100% .005″-.009″ .007″ T110 GF 80%  .005-.008″ .0065″ T110 GF 100% .007″-.009″ .008″ CRA GG 80% .006″-.008″ .007″ CRA GG 100% .005″.009″ .007″ CRA GF 80% .010″-.012″ .011″ CRA GF 100% .007-.012 .0095″

The results indicate that the instant GG coating performed as well or better than GF at loads up to the maximum allowable for the drill pipe considered. It should be noted, the ESD process is less expensive and faster than furnace brazing, and it does not weaken the die block as is observed after a high temperature furnace braze process. Based upon the results it can be concluded a superior rough coating for drill rig tools can be produced at lower cost using the ESD process that does not damage the mechanical properties of the tool blocks (braze). 

I claim:
 1. A die insert, comprising: a substrate; a gripping surface on said substrate, wherein said gripping surface is a textured coating electro-spark deposited on said substrate.
 2. The die insert of claim 1, wherein said textured coating includes a cobalt-based alloy comprising a blend of chromium, carbon, nickel, molybdenum, iron, silicon, and cobalt.
 3. The die insert of claim 2, wherein said blend consists of chromium in the range of 15-40%, cobalt in the range of 40-70%, iron in the range of 1-5%, manganese in the range of 0.1-1.0%, molybdenum in the range of 3-7%, nickel in the range of 1-5%, and less than 1.0% silicon.
 4. The die insert of claim 2, further comprising a hard coating on said textured coating.
 5. The die insert of claim 4, wherein said die insert is formed as a gradient, varying in hardness, respectively, from said substrate to said hard coating.
 6. The die insert of claim 5, wherein said hard coating consists of tungsten carbide in the range of 40.0-97.7%, cobalt in the range of 3.0-30%, 2.0% or less tantalum carbide, 5.1% or less chromium carbide, 4.5% or less chromium, and 5% or less vanadium carbide.
 7. The die insert of claim 3, wherein said blend is supplied by a welding electrode.
 8. The die insert of claim 1, wherein said textured coating is formed to a thickness in the range of 0.001-0.040 inches.
 9. A die insert, comprising: multiple substrates, wherein at least one of said substrates is a die blank and at least one of said substrates is a textured substrate having a gripping surface; said substrates stacked to form a tool block, wherein each said die blank and each said textured substrate are stacked in alternation.
 10. The die insert of claim 9, wherein said gripping surface is a textured coating electro-spark deposited on said substrate.
 11. The die insert of claim 10, wherein said textured coating includes a cobalt-based alloy comprising a blend of chromium, carbon, nickel, molybdenum, iron, silicon, and cobalt.
 12. The die insert of claim 11, wherein said blend consists of chromium in the range of 15-40%, cobalt in the range of 40-70%, iron in the range of 1-5%, manganese in the range of 0.1-1.0%, molybdenum in the range of 3-7%, nickel in the range of 1-5%, and less than 1.0% silicon.
 13. The die insert of claim 9, further comprising a hard coating on said gripping surface.
 14. The die insert of claim 9, wherein said gripping surface is formed to a thickness in the range of 0.001-0.040 inches.
 15. A process for making a die insert, comprising the step of texture-coating a substrate by electro-spark deposition.
 16. The process of claim 15, wherein said substrate is texture-coated in two passes, including a first coating pass and a second coating pass.
 17. The process of claim 16, wherein said first coating pass further comprises the steps of: aligning said substrate on an electro-spark deposition equipment; inserting a welding electrode into said electro-spark deposition equipment; setting an applicator angle in relation to said substrate; and, coating said substrate with said welding electrode.
 18. The process of claim 17, wherein said applicator angle is set in the range of 30 to 40 degrees in relation to said substrate.
 19. The process of claim 16, wherein said second coating pass further comprises the steps of: maintaining said substrate on said electro-spark deposition equipment; setting said applicator angle in the range of 15 to 25 degrees in relation to said substrate; and, coating said substrate with said welding electrode.
 20. The process of claim 15, further comprising the step of hard coating said die insert, wherein said die insert is formed as a gradient, varying in hardness, respectively, from said substrate to said hard coating. 